Aircraft propulsion units of the gas turbine jet type



1955 F. B. HALFORD ETAL 2,725,508

AIRCRAFT PROPULSION UNITS OF THE GAS TURBINE JET TYPE Filed Feb. 25,1952 2 Sheets-Sheet 1 Inventors Frank B. Hal-f rd Eric 5, Mom/1f WilliamH. Arsco'H Attorneys Dec. 13, 1955 F. B. HALFORD ET AL 2,726,503

AIRCRAFT PROPULSION UNITS OF THE GAS TURBINE JET TYPE Filed Feb. 25,1952 2 Sheets-Sheet 2 F/GZ.

I v tor 0 nk B. Ha l fifr d.

I ENC S. Nov/f William H. Arscolrk I Attorneys United States PatefitOAIRCRAFT PROPULSION UNITS OF THE GAS TURBINE JET TYPE Frank BernardHalford, Edgware, Eric Stanley Moult, Hatch End, and William HammettArscott, Harpenden, England, assignors to The De Havilland EngineCompany Limited, Edgware, England, a registered company of Great BritainApplication February 25, 1952, Serial No. 273,265 8 Claims. 01. 60-356)This invention relates to propulsion units of the gas turbine jetpropulsion type including a centrifugal compressor and has for itsobject to provide a propulsion unit which will be capable of giving ahigh degree of thrust in relation to its maximum diameter while being ofa simple and robust nature.

A propulsion unit of the jet propulsion type according to the presentinvention comprises a single entry centrifugal compressor having aforwardly facing inlet eye communicating with a coaxial intake passageacross which extends a ring of whirl-producing vanes for imparting tothe air before it enters the eye rotational motion in the direction ofrotation of the impeller of the centrifugal compressor, a main shaft bywhich the impeller of the centrifugal compressor is connected preferablydirectly to and driven by a single stage or multi-stage turbine disposedin rear of and spaced from the centrifugal compressor, an annular airtransfer passage having an annular entry opening into which the impellerof the centrifugal compressor directly discharges air and an annularexit opening communicating with an annular axial diffuser, an annularcombustion chamber or ring of combustion chambers withwhich the outletend of the axial diffuser communicates, a nozzle ring or the equivalentat the outlet end of the combustion chamber or ring of combustionchambers through which the gases from such chamber or chambers enter theturbine, and a nozzle through which the gases from the turbine aredischarged with propulsive effect.

Conveniently the eye of the centrifugal compressor and the intakepassage are both annular While, moreover, in any case, thewhirl-producing blades or vanes in the intake passage are mounted orformed on an impeller which is arranged to be driven in the samedirection as but at a speed considerably lower than, and preferably atabout half, or rather less than half, the speed of the main shaft.

Thus in one convenient arrangement the whirl-producing impeller isarranged to be driven through gearing from the main shaft, the gearingbeing housed for example within the inner circumferential wall of theannular air intake passage.

In an alternative arrangement the means for driving the whirl-producingimpeller may comprise a turbine rotor separate from the main turbinerotor and acted upon by the gases from the combustion chamber orchambers, said separate turbine rotor being connected to thewhirlproducing impeller.

in any case the whirl-producing impeller is preferably so formed anddriven as to impart to the air in advance of the eye of the centrifugalcompressor a whirling motion in the form of a free vortex, that is tosay a vortex in which the speed of angular movement of the particles ofair is inversely proportional to their distance from the axis ofrotation, although various forms of forced vortex may be used. Owing tolimitations in the design of the vanes 'of the whirl-producing impellerthe mean diameter of the part of the annular intake passage across whichthe vanes of the whirl-producing impeller extend will generally besomewhat greater than the mean diameter of the annular eye of thecentrifugal compressor so that the mean diam eter of the part of theintake passage between the whirlproducing impeller and the eye of thecentrifugal compressor progressively diminishes from the whirl-producingvanes to the eye with a corresponding axial displacement of the adjacentedges of the whirl-producing vanes and the compressor blades to avoidunduly sharp curvature in the walls of said intake passage.

The axial diffuser is conveniently of the form described in thespecification of U. S. Patent application filed December 11, 1950, Ser.No. 200,279, now abandoned, and may or may not be provided with ductsfor the passageof air into or out of the inner circumferential wall ofthe transfer passage for the purpose of boundary layer control to reducethe tendency for turbulence to occur in this transfer passage.

The invention may be carried into practice in various ways but twoconstructions of propulsion unit according to the invention are showndiagrammatically by way of example in the accompanying drawings, inwhich.

Figure 1 is a sectional side elevation of one form of propulsion unitthe section being in a plane containing the axis of rotation of the mainrotary parts of the unit, and

Figure 2 is a similar view to Figure 1 of another form of propulsionunit according to the invention.

In the construction shown in Figure l the propulsion unit comprises acasing or frame A which is of generally tubular form and of taperingcross section from its front to its rear as shown, and carries bearingsindicated at A1 and A2 adjacent to its front and rear ends supporting atubular main shaft assembly B. Secured to the front end of the casing Ais the casing C of a centrifugal compressor of the single entry type therear wall of which is, as shown, substantially fiat while its front wallC1, which includes the entry eye C2 is of curved form viewed in crosssections containing the axis of the compressor so as to provide a smoothcombined axial and radial flow for the air through the compressor inknown manner. The'main shaft B carries at its forward end the combinedaxial and radial flow impeller D of the centrifugal compressor while itsrear end carries the rotor E of a turbine E1 which as shown is of thesingle stage type but may equally be of the multi-stage type.

Rigidly mounted or formed on the front wall C1 of the compressor andforming in effect a continuation of the wall of the inlet eye C2 is awall F constituting the outer wall of an annular intake passage F1 whichextends from an inlet opening F2 at its forward end to the eye C2 and isformed, as shown, so that its diameter first increases progressivelyfrom the inlet opening F2 to a point F3 and then decreases progressivelyto the eye C2.

The inner wall of the intake passage F1 is formed partly by a fixedcasing G, carried by the outer wall by means of suitable webs andprovided with a nosepiece G2, and partly by a rotary wall G1 carried ashereinafter re ferred to, the form of the inner wall G, G1 being such inrelation to that of the outer wall F that the mean diameter of theannular intake passage F1 as a whole increases progressively up to thepoint P3 and then decreases'progressively to the eye C2.

Extending across the annular intake passage F1 at the point P of largestmean diameter are the blades H of a whirl-producing impeller H1 which issupported on a hub member H2 carried in hearings in the casing G andalso supporting the rotary part G1 of the inner wall of the annularintake passage F1 which thus rotates as a unit with the impeller H1. I Y

The impeller H1 and wall part G1 are arranged to be driven at about halfor rather less than half the speed of the impeller D of the centrifugalcompressor through reduction gearing comprising a relatively small sunwheel K connected by a shaft K1 to the impeller D and meshingwithrelatively large planet wheels K2 secured to shafts K3 supported instationary bearings, the shafts K3 also carrying further relativelysmall sun wheels K4 which mesh with a relatively large sun wheel K5 onthe hub H2.

Immediately surrounding the casing of the centrifugal compressor C is anannular transfer passage L, which viewed in the cross section shownresembles a right angle bend of comparatively small mean radius. Thisradius is chosen to be as small as is practicable without risk ofcausing undue turbulence in the air due to separation of the fluid flowfrom the inner wall of the bend. Passages (not shown) for the inflow oroutflow of air through appropriately placed ducts in the inner wall ofthe bend for boundary layer control purposes may be provided asdescribed in the specification of U. S. patent application No. 200,272,now abandoned, so as to enable a smaller radius of curvature to be usedthen would otherwise be possible.

The annular inlet opening L1 of the transfer passage L receives airdirect from the impeller D while the annular outlet opening L2, whichfaces rearwardly, communicates directly with the forward end of anannular axially extending diffuser M in the form of an annular passagecontaining a set or two or more sets of guide vanes indicated at M1which convert at least the major portion of the rotational energy of theair entering the diffuser into pressure energy, thus acting asstraighteners. The diffuser is thus conveniently of the kind describedin the specification of U. S. patent application No. 200,279, nowabandoned.

The rear end of the axial diffuser M communicates with an annular airdelivery passage M2 or series of air delivery passages by which the airis led to a series of substantially axially extending combustionchambers N lying around the smaller diameter part of the casing A sothat the over all diameter of this part of the unit is not greater than,and is preferably somewhat less than the over all diameter of thediffuser. The combustion chambers N, which may be of known form and maybe supplied with fuel in any convenient manner, communicate at theirrear ends with a nozzle ring N1 through which the hot gases from thecombsution chambers are directed onto the blades of the turbine rotor E,the gases after passing through the turbine being led by a suitablyformed annular duct NZ to a propulsion nozzle N3.

In the alternative construction shown in Figure 2 the arrangement isgenerally similar to that shown in Figure 1 and similar parts havetherefore been given similar reference letters to the correspondingparts in Figure l and will not be again described.

The principal difference between the construction shown in Figure 2 andthat shown in Figure l is that, instead of the whirl-producing impellerH1 being driven through gearing from the impeller D of the centrifugalcompressor it is driven by a separate turbine rotor. Thus, in theconstruction shown in Figure 2, the whirl-producing impeller H1 ismounted upon or provided with a hub H3 rigidly supported on the frontend of a shaft 0 which passes through a suitably modified main shaft Blcarrying the impeller D and the turbine rotor E and carries at its rearend a turbine rotor P disposed in rear of the rotor E and on which thegases from the combustion chambers impinge after leaving the rotor E andafter passing through a set of stationary vanes P1 so as to causerotation of the shaft 0 in the same direction as the main shaft B1 butat about half or somewhat less than half the speed of the main shaft Bl.

As shown the shaft 0 is supported in bearing D in a plate D within thecasing G and in bearings O mount ed inthe ends of the shaft B1.

being arranged with their axes parallel to the axis of the shaft B theiraxes may have a tangential component and in this case the dijfuserblades M1 maybe so formed as to cause the air to leave them in a similarcombined axial and tangential direction so that the air can enter thecombustion chambers with as little change in direction as possible.

It is, moreover, to be understood that, although in the arrangementshown a series of combustion chambers are provided the invention is alsoapplicable to arrangements in which a single annular combustion chambersurrounds the main casing.

Moreover, in modified arrangements according ot the invention thecentrifugal compressor may have an impeller the blade carrying disc ofwhich instead of havhelix.

ing a substantially flat outer portion hasan outer portion ofapproximately frusto-conical form so that the air leaves it in adirection having a substantial rearward axial component, thus reducingthe angle through which the air has to be deflected by the transferpassage to enter the diffuser.

It will be seen that with each of the arrangements shown according tothe invention the whirl-producing impeller H1, by causing the airdelivered to the eye C2 to rotate in the same direction as the impellerD, enables a higher rate of mass flow to be obtained through thecentrifugal compressor without exceeding the permissible Mach number ofthe fluid flow relatively to the blades of the impeller D. Moreover, theair will leave the centrifugal impeller D with a high rotationalcomponent of motion and will thus readily be able to pass through thetransfer passage L in spite of the apparent sharpness of the bend inthat passage when viewed in the cross sections shown since each particleof air will be passed through the bend in a path resembling a spiral Therotational energy of the particles of air can then be converted intopressure in the axial diffuser M, which itself is of small over alldiameter compared with a radial flow diffuser of similar capacity, andthe maximum diameter and weight of the unit can thus be maintained smallfor the maximum rate of mass flow through it and hence the maximumthrust which can be obtained from it.

What we claim as our invention and desire to secure by Letters Patentis:

1. An aircraft propulsion unit of the jet propulsion type comprising asingle entry centrifugal compressor having a forwardly facing inlet eye,a rotary whirl-producing impeller arranged in an entry passage inadvance of the entry eye of the compressor and driven in the samedirection as but at a lower speed than the centrifugal impeller, thewhirl-producing impellerhaving an annular ring of rotary vanes whichhave a mean diameter appreciably greater than the diameter of the entryeye of the compressor, while the diameter of the entry passageprogressively diminishes from the whirl-producing impeller vanes to theentry eye of the compressor, a turbine disposed in rear of and spacedfrom the centrifugal compressor, a main shaft by which the impeller ofthe centrifugal compressor is connected to and driven by said turbine,an annular axial diffuser in rear of said compressor, an annular airtransfer passage leading from the compressor to said annular axialdiffuser, the transfer passage regarded in cross-sections containing theaxis of the compressor being bent through a substantial angle from agenerally radial direction to a generally axial direction, and beingunencumbered with any blades upstream of the axial portion of thetransfer passage which would tend to convert the circumferentialcomponent of the velocity of the gas into a radial or axial component,at least one combustion chamber with which the outlet end of the axialdiffuser communicates, a nozzle ring at the outlet end of the combustionchamber through which the gases from such chamber enter the turbine, anda nozzle through which the gases from the turbine are discharged withpropulsive effect.

2. A propulsion unit as claimed in claim 1, in which the Whirl-producingimpeller is arranged to impart rotation to the air passing through theentry passage Without exercising upon it any appreciable compressingeffect.

3. A propulsion unit as claimed in claim 1 in which the bend in thetransfer passage between the centrifugal compressor and the axialdiffuser occurs at or closely adjacent to the circumferential tips ofthe centrifugal compressor blades.

4. A propulsion unit of the jet propulsion type as claimed in claim 1 inwhich the means for driving the Whirl-producing impeller comprisestransmission gearing connecting the Whirl-producing impeller to the mainshaft.

5. A propulsion unit of the jet propulsion type as claimed in claim 4 inwhich the transmission gearing is housed within the innercircumferential Wall of the annular intake passage.

6. A propulsion unit of the jet propulsion type as claimed in claim 5 inwhich the whirl-producing impeller is formed and driven at such speed asto impart to the air in advance of the eye of the centrifugal compressora whirling motion in the form of a substantially free vortex.

7. A propulsion unit of the jet propulsion type as claimed in claim 1including a subsidiary turbine rotor separate from the turbine rotorwhich drives the impeller of the centrifugal compressor and acted uponby the gases from the combustion chamber, and transmission means betweenthe subsidiary turbine rotor and the Whirlproducing impeller.

8. A propulsion unit of the. jet propulsion type as claimed in claim 7in which the whirl-producing impeller and the turbine rotor driving itare so formed that the Whirl-producing rotor imparts to the air inadvance of the eye of the centrifugal compressor a whirling motion inthe form of a substantially free vortex.

References Cited in the file of this patent UNITED STATES PATENTS2,405,919 Whittle Aug. 13, 1946 2,423,634 Berliner July 8, 19472,446,552 Redding Aug. 10, 1948 2,458,600 lrnbert et al Ian. 11, 19492,464,724 Sdille Mar. 15, 1949 2,548,465 Burdett et al Apr. 10, 19512,575,682 Price Nov. 20, 1951 FOREIGN PATENTS 611,447 Great Britain Oct.29, 1948

